I think the method for drawing tires in this lesson is a lil misleading. In the 2nd step we are told to break away from the traditional cylinder, by by making it a lil more "bubbly". Now this is not incorrect way to draw tires, but only for motorcycle tires (and also bike tires). Car tires are flat (also tractor tires). It comes down to that motorcyles need to be "bubbly" for the veahile to turn easier. Car tires need to be flater to grip the ground better and nice give out the weight. Now its not impossible to find exeptions to this rule, but they are exeptions and i dont think this is what the lesson was about. I dont want to be a smartass or something, but i really think this challange instructions should be redone or at least change the narration to be about drawing motorcycle tires.